In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, transmission schemes and reception schemes based on the use of narrow beams might be needed at high frequencies to compensate for propagation losses. For a given communication link, a beam can be applied at both the network side (such as at the transmission and reception point (TRP) of a network node) and the user side (such as at terminal devices served by the network node). A beam pair link (BPL) is defined by the beam used by the TRP (denoted TRP beam) for communicating with the terminal device and the beam used by the terminal device (denoted UE beam) for communicating with the TRP. Each of the TRP beam and the UE beam could be used for any of transmission and reception. Likewise, there could be separate BPLs for downlink communications (where the TRP beam is a transmission (TX) beam and where the UE beam is a reception (RX) beam) and uplink communications (where the TRP beam is an RX beam and where the UE beam is a TX beam).
In general terms, a beam management procedure is used to discover and maintain BPLs. A BPL is expected to be discovered and monitored by the network using measurements on downlink reference signals used for beam management, such as channel state information reference signals (CSI-RS). The CSI-RS for beam management can be transmitted periodically, semi-persistently or aperiodic (such as being event triggered) and they can be either shared between multiple terminal devices or be device-specific.
In order to find a suitable TRP beam the TRP transmits CSI-RS in different TRP TX beams on which the terminal devices performs reference signal received power (RSRP) measurements and reports back the N best TRP TX beams (where the value of N can be configured by the network). Furthermore, the CSI-RS transmission on a given TRP TX beam can be repeated to allow the terminal device to evaluate suitable UE beams, thus enabling so-called UE RX beam training.
If the TRP has dual-polarized antennas, each CSI-RS resource will typically be configured with two antenna ports, one antenna port per polarization, such that the terminal device can measure average RSRP over both polarizations and hence reduce the risk of polarization mismatch. Another advantage with two-port beam management is that the terminal device can choose the best beam not only based on highest RSRP, but also consider parameters such as rank, user throughput, etc. One reason for choosing CSI-RS as the reference signal for beam management is that the terminal device can then directly report preferred CQI, rank and precoder after a beam management procedure, which will reduce the latency between a beam management procedure and data transmission.
It is envisioned that for some TRPs having two or more antenna arrays, or panels, these two or more antenna arrays, or panels, might be simultaneously used. It is further envisioned that two antenna arrays, or panels, might be simultaneously used for beam management purposes. But there are not any existing mechanisms that disclose, or envision, how such a beam management process would be implemented.
Hence, there is still a need for an improved beam management, especially when two antenna arrays, or panels, simultaneously are used.